Where is retention cutoff date defined?

We are running into space issues with the built-in nuget repo and it doesn’t appear to be removing old releases.

There are a lot of entries like this one:
ReportingService.1.0.0.1783 was published on 5/23/2016 8:43:04 PM +00:00. It will be kept. Reason: published after the cutoff date.

Where/how is this cutoff date defined?

I found this. It is in library > Packages on the right side. There is Repository retention in days.